title: Tagging of cardiac magnetic resonance images in the polar coordinate system: physical principles and practical implementation.
abstract: OBJECTIVE
  In current magnetic resonance practice, myocardial tagging is implemented by laying down a rectilinear presaturation grid over the heart. Although both the geometry and the deformation of the heart are better described in the polar coordinate system, practical methods for laying down polar grids have been elusive. The theory and implementation of high-density tagging in the polar coordinate system is described in this study.
  
  
  METHODS
  Tagging sequences for generating high-density tagging patterns in both radial and circular directions have been developed. The approach, theoretical basis, and experimental results of the suggested sequences for efficient polar tagging are described in this article.
  
  
  RESULTS
  A 10-ms preparation tagging sequence was tested for generating compact radial and circular tag patterns in a magnetization preparation time comparable to binomial rectilinear grid tagging. The sequence was successfully tested on both phantoms and human subjects.
  
  
  CONCLUSIONS
  Direct myocardial tagging in the polar coordinate system is practical in acquisition times similar to Cartesian tagging. The deformation patterns of radial and circular tag lines can be used to isolate and analyze the circumferential and radial components of myocardial motion. Further work remains to establish the reliability and robustness of the techniques for a variety of clinical applications.
authors.affiliation: Department of Biomedical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran; Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.
authors.forename: Abbas
authors.initials: A
authors.lastname: Nasiraei-Moghaddam
authors.forename: J Paul
authors.initials: JP
authors.lastname: Finn
mesh_terms: D000465:Algorithms; D009202:Cardiomyopathies / Q000473:pathology* / Q000503:physiopathology*; D055119:Elastic Modulus; D054459:Elasticity Imaging Techniques / Q000379:methods*; D006352:Heart Ventricles / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: circular tagging; myocardium; polar coordinate system; radial tagging; strain